1. Technical Field
The present invention relates to a piezoelectric element made of a piezoelectric film and electrodes, a liquid ejecting head and a liquid ejecting apparatus which include the piezoelectric element and discharges liquid droplets from a nozzle opening.
2. Related Art
As a representative example of a liquid ejecting head, a part of a pressure generating chamber that communicates with a nozzle for discharging ink droplets is composed of a vibration plate, the vibration plate is deformed by a piezoelectric element, and ink of the pressure generating chamber is discharged, as ink droplets, from the nozzle by pressuring the ink. As the piezoelectric element used in the ink jet recording head, it is a piezoelectric film made from a piezoelectric material with an electromechanical transducing function, for example, a crystallized piezoelectric film and electrodes put on the both side of the piezoelectric film.
As methods of forming piezoelectric film, there are chemical solution methods, such as sol-gel, MOD (Motel Organic Deposition) method and so on, and physical method, such as sputtering method. Piezoelectric film can be created using these methods. For example, in case of using sol-gel method, organic metal compounds are dissolved in solvent to form colloidal solution, then it is coated on a substrate, the formed film is heated and crystallized to form a piezoelectric film.
Generally, a lead-based piezoelectric material represented by, for example, PZT (lead zirconate titanate) has been used for such a piezoelectric element (for example, see JP-A-2001-223404). However, from the viewpoint of environmental issues, a lead-free piezoelectric material or a piezoelectric material with a reduced amount of lead is required. As the lead-free piezoelectric material, a barium titanate-based composition oxide has been known for a long time (see JP-A-62-154680).
However, barium titanate-based composition has been mainly used as a piezoelectric bulk material. There is almost no practical study on barium titanate-based piezoelectric film formed by chemical method or physical method. In addition, barium titanate-based bulk is fabricated by mixing powder of metal oxides or metal carbonate at first, then calcining, grinding, forming the mixture and firing the formed body at 1000-1400° C., finally forming electrode on polished both side of the bulk. Therefore, stress caused by volume expansion and contraction of the ceramic at the time of manufacture is significantly small compared with that caused at the time of forming a piezoelectric film on a substrate by chemical solution method or sputtering method.
If the barium titanate-based material is used for a piezoelectric film on a substrate, there is a problem in that displacement is significantly small compared with that of the above-described PZT. It is also desirable to meet the needs of increasing density of barium titanate-based film, firing the film at low temperature and improving dielectric breakdown even when a high voltage is applied. That is to say, it is desirable to improve electric strength and so on. In addition, these problems are not only limited to liquid ejecting head represented by an ink jet recording head, but also exist in other piezoelectric elements.